The spells to find these new Wizards were lost with the destruction of the governmental buildings and schools. So now there was no way to reach those new Wizards and Witches to tell them about the Magic community and to show them how to use their magic. Any infants born now were sports, one-off flukes whose accidental magic would end up killing them when it finally revealed them to the now-virulently anti-magic Muggle governments. And any who did survive would marry a non-magical spouse and eventually the gene that allowed for magic would disappear from the gene pool.
The magical species — centaurs, giants, trolls, and so forth — had simply been wiped out. They usually inhabited isolated locations with no shielding whatsoever. Tactical nukes finished them off handily. Not even the Goblins and Dwarves could survive a nuke driven deep into their tunnels by a Muggle-born suicide squad intent on revenge against all things magical for destroying their families.
The Muggle world was licking its wounds. The Magic War had done something nothing else had — united the various warring Muggle tribes into a cohesive whole. That cooperation, of course, would soon break apart into disagreeing factions. But the war had shown they could work together against a common enemy, no matter their individual differences. That experience would temper future disagreements, and help keep them focused on finding and eliminating any new Wizards or Witches. Mitigating the environmental damage of the war, ironically, were the few surviving Muggle-born Wizards and Witches who were using their magic to clean up the radioactive bombing sites and restoring them to usefulness.
And to think, it all began to unravel because of one selfish "pig-stupid" Weasley: Ronald the Jealous Git.
His brother, Bill, had taken him in after he had left Harry and Hermione in the Forest of Dean during what should have been their seventh year at Hogwarts. He had watched the boy mope around his apartment for weeks. Misunderstanding the boy's inherent laziness as guilt, Bill had taken him to dinner at the Leaky Cauldron. He had planned to console Ron with his favourite activity — eating. When Bill tried to persuade him to "let out his guilt," Ron had angrily shouted the details of their secret horcrux-hunting mission in the crowded pub.
Harry blamed Dumbledore for that situation. If the man hadn't been so close-mouthed about his secrets, if he had spoken plainly to Harry instead of in riddles and questions, if he hadn't wasted months and years doing nothing, the original search wouldn't have taken so long. And Ron wouldn't have been able to betray them. Instead, after the bumbling Wizard's death, they had wasted valuable time wandering in the wilderness looking for things he should have been searching for and destroying before Harry had ever heard of Hogwarts!
And just what had the Headmaster been planning? Either he was senile, incompetent, or a sociopathic master manipulator who enjoyed playing with other's lives, never really understanding or caring about the pain and heartache he created. Or how much he risked in not sharing what he knew. And why hadn't he taught Harry any valuable fighting skills? That lapse alone had added years to his fighting with Voldewhore.
Naturally, a Death Eater, or a sympathizer, had overheard Ron's wobbler at the Leaky Cauldron.
Lord Voldewhore immediately retrieved and re-hid his remaining horcruxes – Hufflepuff's Cup and Ravenclaw's Diadem – behind fidelius charms. In typical Voldewhore fashion, he left taunting messages and traps in place of the former horcruxes. It had been spirit-crushing to break into the Lestrange Vault and discover that it was all for nothing. Going after the Diadem at Hogwarts was where Hermione had been cursed. The Withering Curse was unstoppable, just as it had been when it killed the Headmaster. Harry's quick reaction in cutting off her arm an instant later had saved her life, but only temporarily. It took her five long pain-filled years to die.
Riddle moving those last two Horcruxes cast the Wizarding World into the abyss with Magical and Muggle world suffering alike. It had taken Harry seven more years to destroy the horcruxes, with friends and allies dying at his side, while he killed Voldewhores's followers whenever and wherever he found them.
Voldewhore didn't care whom else died — he was immortal! But with tremendous determination and tenacity, Harry had fought on, watching his friends and allies die one-by-one. He reluctantly became the Master of Death and used Death's help to locate and destroy the final horcrux — himself. And then killed Tom with Gryffindor's Sword while the git was celebrating his "victory" over Harry.
Death had enjoyed the feast provided by the war. Not even Joseph Stalin's and Mao Zedong's Communist purges had yielded such a bonus of Wizardly deaths. It gladly helped Harry Potter to his victory, and gained the long-awaited soul of Tom Marvolo Riddle. Why would it not enjoy this? Both the boy and his nemesis had provided it with a plethora of souls and activity. But it had lost its freedom to Harry Potter. And was looking at being terminally bored for thousands of millennia to come. The second was annoying, but the first was intolerable. No one was allowed to escape DEATH!
Now all Death had to do was trick Harry into giving up his Mastery. Harry Potter was a master of many arts, but no one is more cunning than Death.
One day, Death presented itself to its Master. Harry was sitting on a park bench in a bomb-blasted radiation-ruined town destroyed by an errant nuclear shelling, lost in his thoughts of self-loathing at losing everyone and everything he held dear. He berated himself for not doing more sooner, for not preventing the disaster that destroyed Wizardkind. Living held no appeal, and being the Master of Death meant he couldn't die. He couldn't even get rid of the items by throwing them through the Veil of Death in the Ministry — Voldewhore had destroyed it fearing Harry might use it to kill him. And the damn things could withstand a nuclear blast!